Effect of cold rolling on pitting resistance in duplex stainless steels

Abstract

Duplex Stainless Steels (DSS) are biphasic austeno-ferritic steels in which the best combination of mechanical
and corrosion-resistance properties is achieved for almost equal volume fractions of the phases. These steels
are classifi ed according to their pitting corrosion resistance, assessed by the PREN index (Pitting Resistance
Equivalent Number) which, although qualitatively, is widely employed as comparison. The present work is
aimed to study the pitting resistance of four DSS grades (SAF 2101, 2304, 2205 and 2507) in the as-received
conditions and after cold rolling at various thickness reductions (from 15% to 85%), to highlight the effects of
cold working on the corrosion behaviour. The materials were potentiodynamically tested in artifi cial seawater
(pH 7) and the corresponding Critical Pitting Temperatures (CPT) were determined. Cold deformation mainly
affected the Lean DSS grades, whereas the high-alloyed DSS were stable, even after heavy deformations.
These differences can be attributed not only to composition but also to the onset of diffusionless phase
transformations induced by cold working, which make the materials more prone to corrosive attacks.